Re: RFR: 8318776: Require supports_cx8 to always be true [v7]
On Thu, 23 Nov 2023 12:09:27 GMT, David Holmes wrote: >> As discussed in JBS all platforms (some tweaks to Zero are in progress) >> actually do support `cx8` i.e. 64-bit compare-and-exchange, so we can strip >> out the locked-based alternatives to using it and just add a guarantee that >> it is true at runtime. And all platforms except some ARM variants set >> `SUPPORTS_NATIVE_CX8`, so we can greatly simplify things. Summary of changes: >> - `_supports_cx8` field is only needed when `SUPPORTS_NATIVE_CX8` is not >> defined >> - Assertions for `supports_cx8()` are removed >> - Compiler predicates requiring `supports_cx8()` are removed >> - Access backend is greatly simplified without the need for lock-based >> alternative >> - `java.util.concurrent.AtomicLongFieldUpdater` is simplified without the >> need for a lock-based alternative >> >> I did consider moving all the ARM `kuser_helper` related code to be only >> defined when `SUPPORTS_NATIVE_CX8` is not defined, but there was a >> theoretical risk this could change the behaviour if ARMv7 binaries were run >> on other ARM CPU's. I added a note to that effect in >> vm_version_linux_arm32.cpp so the ARM port maintainers could clean this up >> further if desired. >> >> Testing: >> - All Oracle tiers 1-5 builds (which includes an ARMv7 build) >> - GHA builds/tests >> - Oracle tiers 1-3 sanity testing >> >> Zero changes coming in via >> [JDK-8319777](https://bugs.openjdk.org/browse/JDK-8319777) will be merged >> when they arrive. >> >> Thanks. > > David Holmes has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains ten commits: > > - Merge > - Fix typo > - Merge with master and update Zero code accordingly > - Merge branch 'master' into 8318776-supports_cx8 > - Remove unnecessary includes of vm_version.hpp. >Fix copyright years. > - Remove cx8 comment as no longer relevant (the spinlock is used regardless > of cx8) > - Remove suports_cx8() checks from gtest > - Remove test for VMSupportsCX8 > - 8318776: Require supports_cx8 to always be true Thanks for all the reviews. Integrating now. - PR Comment: https://git.openjdk.org/jdk/pull/16625#issuecomment-1824966904
Re: RFR: 8318776: Require supports_cx8 to always be true [v7]
> As discussed in JBS all platforms (some tweaks to Zero are in progress) > actually do support `cx8` i.e. 64-bit compare-and-exchange, so we can strip > out the locked-based alternatives to using it and just add a guarantee that > it is true at runtime. And all platforms except some ARM variants set > `SUPPORTS_NATIVE_CX8`, so we can greatly simplify things. Summary of changes: > - `_supports_cx8` field is only needed when `SUPPORTS_NATIVE_CX8` is not > defined > - Assertions for `supports_cx8()` are removed > - Compiler predicates requiring `supports_cx8()` are removed > - Access backend is greatly simplified without the need for lock-based > alternative > - `java.util.concurrent.AtomicLongFieldUpdater` is simplified without the > need for a lock-based alternative > > I did consider moving all the ARM `kuser_helper` related code to be only > defined when `SUPPORTS_NATIVE_CX8` is not defined, but there was a > theoretical risk this could change the behaviour if ARMv7 binaries were run > on other ARM CPU's. I added a note to that effect in > vm_version_linux_arm32.cpp so the ARM port maintainers could clean this up > further if desired. > > Testing: > - All Oracle tiers 1-5 builds (which includes an ARMv7 build) > - GHA builds/tests > - Oracle tiers 1-3 sanity testing > > Zero changes coming in via > [JDK-8319777](https://bugs.openjdk.org/browse/JDK-8319777) will be merged > when they arrive. > > Thanks. David Holmes has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits: - Merge - Fix typo - Merge with master and update Zero code accordingly - Merge branch 'master' into 8318776-supports_cx8 - Remove unnecessary includes of vm_version.hpp. Fix copyright years. - Remove cx8 comment as no longer relevant (the spinlock is used regardless of cx8) - Remove suports_cx8() checks from gtest - Remove test for VMSupportsCX8 - 8318776: Require supports_cx8 to always be true - Changes: https://git.openjdk.org/jdk/pull/16625/files Webrev: https://webrevs.openjdk.org/?repo=jdk=16625=06 Stats: 460 lines in 39 files changed: 16 ins; 429 del; 15 mod Patch: https://git.openjdk.org/jdk/pull/16625.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16625/head:pull/16625 PR: https://git.openjdk.org/jdk/pull/16625
